The present invention relates generally to shock absorbing apparatus. In particular, the present invention relates to shock absorbing apparatus operable to provide dissipation of forces imposed upon a dock, floating platform, offshore oil rig, or the like, which may occur as a result of impact by a floating vessel such as a barge, crew boat or the like. The present invention will find particular utility in connection with boat bumpers for offshore platforms, but, as will become apparent, the apparatus of this invention may have wide applicability extending beyond such offshore uses.
In an exposed environment such as an oil well platform located many miles offshore, severe weather conditions impose a variety of problems. For example, high winds and large waves may make the docking of a barge or other vessel to the offshore platform extremely difficult and hazardous. During adverse weather conditions the vessel may rub against the platform with great force, or the action of the wind and the sea may be of sufficient force to effect a collision between the vessel and the docking facility which may result in great damage to the platform and vessel as well as injury to personnel aboard the platform. The vessel may be punctured by such a collision and may sink or otherwise be severly damaged.
A collapse or displacement of a portion of the platform due to a collision may impede oil drilling or producing activities with severe adverse economic consequences. If gas or oil lines are ruptured by such collision, explosion or fire may result. In addition, a rupturing of such lines can result in ecological damage along a shoreline many miles away.
In order to reduce the undesirable effects of collision between a floating vessel and a docking facility, bumpers are used on both vessels and docking facilities to cushion impact and protect the surfaces coming into contact during such collisions. In the past, old automobile tires were placed around the periphery of loading docks in order to reduce the adverse effects of impact. More recently, cushioned bumpers which have been shock mounted upon such platforms have been used. However, in an offshore environment during extreme weather conditions, a beam sea could drive a vessel against a platform with such force that presently known arrangements would no longer serve to prevent serious damage to the vessel or to the platform.
It is known to mount bumpers upon shock absorbing devices on offshore platforms which arrangement serves to dissipate the forces imposed upon the platform when a vessel collides with a bumper. Such arrangements generally comprise a substantially vertically disposed elongate cushioning element which is positioned to lie partially below and partially above the mean water line. These cushioning devices, which usually comprise a rod covered by some rubber-like cushioning material, are attached at their upper ends to the platform through a shock absorber of some kind. The bottom of the cushioning element, or rod, is either anchored, pivotably mounted or shock mounted to the platform below the level of the water.
A shock absorber or shock cell used in conjunction with offshore platform bumpers may be required to absorb forces in the order of 100 tons or so. Therefore, such shock cells must have great structural integrity without being economically impractical.
In addition, such a shock cell must be corrosion resistant to salt water and to those contaminants which may accidently spill into the environs of the platform during drilling or producing operations. This is particularly the case for a shock cell positioned below the water line around the platform. Moreover, a shock cell for use in conjunction with an offshore platform is desirably maintenance free and of high reliability to minimize the occurrences of damage to the platform as a result of shock cell failure. Ordinarily, shock cells and bumpers are placed on a platform before the platform is positioned in a body of water. After a platform has been situated offshore, maintenance or replacement of a shock cell can be most cumbersome and require much more time and expense than required during initial assembly.